A prior art document, Japanese Patent Laying-Open No. 8-159633 (PTD 1), discloses a cryogenic apparatus for a superconducting magnet where liquid helium is used as cryogenic coolant, the cryogenic apparatus uniformly cooling radiation shields so as to suppress an increase in amount of heat intrusion into a cryogenic coolant tank. In the cryogenic apparatus disclosed in PTD 1, a radiation-shield cooling pipe is composed of a plurality of radiation-shield cooling pipes constituted of parallel flow paths. Each of the radiation-shield cooling pipes constituted of parallel flow paths is provided with a flow rate control valve around its exit which is varied in position with a change in temperature of the coolant flowing in the flow path.
A prior art document, Japanese Patent Laying-Open No. 2000-105072 (PTD) 2), discloses a multi-circulation type liquid helium recondensation apparatus that cools a helium storage tank with sensible heat of helium gas. A prior art document, Japanese Utility Model Laying-Open No. 3-88366 (PTD 3), discloses a superconducting magnetic shield that cools a radiation shield with sensible heat of helium gas.
In the multi-circulation type liquid helium recondensation apparatus disclosed in PTD 2, a major part of the helium gas is cooled to about 40 K by a first heat exchanger of a small-sized refrigerator while positions of flow rate regulating valves are being adjusted, and the cooled helium gas is supplied into the liquid helium storage tank through a flow path. The rest of the helium gas is liquefied through the first heat exchanger and a second heat exchanger of the small-sized refrigerator, and the liquid helium is supplied into the liquid helium storage tank through a flow path.
In the superconducting magnetic shield disclosed in PTD 3, a heat transfer plate is disposed on the outer side of a liquid helium container in such a way as to surround the liquid helium container, and pipes for the passage of helium gas are provided in contact with the outer peripheral surface of the heat transfer plate.